Numbers 3:39

36 And under the custody and charge of the sons of Merari shall be the boards of the tabernacle, and the bars thereof, and the pillars thereof, and the sockets thereof, and all the vessels thereof, and all that serveth thereto,

37 And the pillars of the court round about, and their sockets, and their pins, and their cords.

38 But those that encamp before the tabernacle toward the east, even before the tabernacle of the congregation eastward, shall be Moses, and Aaron and his sons, keeping the charge of the sanctuary for the charge of the children of Israel; and the stranger that cometh nigh shall be put to death.

39 All that were numbered of the Levites, which Moses and Aaron numbered at the commandment of the LORD, throughout their families, all the males from a month old and upward, were twenty and two thousand.

40 And the LORD said unto Moses, Number all the firstborn of the males of the children of Israel from a month old and upward, and take the number of their names.

41 And thou shalt take the Levites for me (I am the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel.

42 And Moses numbered, as the LORD commanded him, all the firstborn among the children of Israel.